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United States Patent |
6,118,034
|
Vicari
,   et al.
|
September 12, 2000
|
Process for the selective hydrogenation of dienes in reformate flows
Abstract
In the process for the selective hydrogenation of dienes in
diene-containing feed streams, a diene-containing feed stream is
hydrogenated over a nickel-containing precipitated catalyst at from 40 to
100.degree. C., a pressure of from 3 to 20 bar and a WHSV (weight hourly
space velocity) of from 1 to 10 kg/(l.times.h) in the presence of free
hydrogen.
Inventors:
|
Vicari; Maximilian (Limburgerhof, DE);
Walter; Marc (Frankenthal, DE);
Schwab; Ekkehard (Neustadt, DE);
Muller; Hans-Joachim (Grunstadt, DE);
Kons; Germain (Mannheim, DE);
Dilling; Stephan (Edingen-Neckarhausen, DE);
Polanek; Peter (Weinheim, DE)
|
Assignee:
|
BASF Aktiengesellschaft (Ludwigshafen, DE)
|
Appl. No.:
|
142217 |
Filed:
|
September 3, 1998 |
PCT Filed:
|
February 27, 1997
|
PCT NO:
|
PCT/EP97/00960
|
371 Date:
|
September 3, 1998
|
102(e) Date:
|
September 3, 1998
|
PCT PUB.NO.:
|
WO97/32944 |
PCT PUB. Date:
|
September 12, 1997 |
Foreign Application Priority Data
| Mar 04, 1996[DE] | 196 08 241 |
Current U.S. Class: |
585/262; 585/259; 585/261; 585/263; 585/264; 585/274; 585/276 |
Intern'l Class: |
C07C 005/03 |
Field of Search: |
585/259,261,263,264,274,276
|
References Cited
U.S. Patent Documents
2906790 | Feb., 1959 | Smyth | 260/677.
|
4659687 | Apr., 1987 | Cymbaluk | 502/207.
|
5417844 | May., 1995 | Boitiaux et al. | 208/143.
|
5736484 | Apr., 1998 | Polanek et al. | 502/349.
|
Foreign Patent Documents |
466567 | Jan., 1992 | EP.
| |
672452 | Sep., 1995 | EP.
| |
685552 | Dec., 1995 | EP.
| |
2 131 043 | Jun., 1984 | GB.
| |
Other References
Ullmann's Enc. of Ind. Chem., vol. A3, 5th Edition, p. 490, 1985.
|
Primary Examiner: Yildirim; Bekir L.
Attorney, Agent or Firm: Keil & Weinkauf
Claims
We claim:
1. A process for the selective hydrogenation of dienes in diene-containing
feed streams, which comprises hydrogenating such a diene-containing feed
stream over a nickel-containing precipitated catalyst at from 40 to
100.degree. C., a pressure of from 3 to 20 bar and a WHSV of from 1 to 10
kg/(l.times.h) in the presence of free hydrogen, wherein the catalyst
comprises from 65 to 80% of nickel, from 10 to 25% of silicon, from 2 to
10% of zirconium, from 0 to 10% of aluminum, all components calculated as
oxides and percentages by weight based on the total mass of the catalyst,
with the proviso that the sum of the content of silicon dioxide and
aluminum oxide is at least 15%.
2. A process as claimed in claim 1, being conducted at from 50 to
80.degree. C., a pressure of from 5 to 12 bar and a WHSV of from 3 to 7
kg/(l.times.h).
3. A process as claimed in claim 1, wherein the feed stream comprises from
15 to 90% by weight of aromatics and up to 5000 ppm by weight of dienes.
4. A process as claimed in claim 1, wherein the hydrogen is fed into the
hydrogenation step in such a way that its amount is regulated as a
function of the dienes to be hydrogenated, being from 1 to 1.3 mol of
hydrogen per mol of diene structure in the feed stream.
5. A process as claimed in claim 1, wherein hydrogenated product is
separated in an extractive distillation step into an aromatic hydrocarbon
mixture and a non-aromatic hydrocarbon mixture.
6. A process as claimed in claim 1, wherein the aromatic content of the
feed stream is increased prior to the selective hydrogenation by means of
one or more upstream distillation, extraction and/or extractive
distillation steps.
Description
The present invention relates to a process for the selective hydrogenation
of dienes, in particular of dienes in reformate streams (feed streams)
over a nickel-containing precipitated catalyst. In addition, the present
invention relates to a process for preparing high-purity aromatics or
aromatic mixtures.
The reformate produced by catalytic reforming of naphtha represents a very
important source of aromatics for isolating pure aromatics. Important
constituents of the reformate stream are aromatic compounds such as
benzine, toluene, xylene and ethylbenzene. The boiling range of the
hydrocarbon mixture is between 60 and 180.degree. C. Apart from the
saturated hydrocarbons and aromatic compounds, the untreated reformate
streams contain other constituents such as olefins and diolefms. To
further process them to give pure aromatics, up to now a series of
distillation, extraction and extractive distillation steps were used.
If high purities are required, the diene compounds which are difficult to
separate off by means of the abovementioned physical processes have to be
removed from the pure aromatic fraction. According to Ullmann's
Encyclopedia of Industrial Chemistry, 5th Edition, Vol. A3, Page 490,
Verlag Chemie, this is carried out by further treating the pure aromatics
over an active alumina: on passing through the fixed bed, the diene
compounds are selectively adsorbed. Disadvantages of this process are the
high solids consumption and the necessity of disposing of the alumina
contaminated with hydrocarbon compounds, disadvantages which are becoming
increasingly important in line with ever stricter environmental controls.
An alternative process comprises the selective hydrogenation of traces of
unsaturated compounds. FR-A 2 720 754 discloses, in the case of pyrolysis
gasoline, selectively hydrogenating dienes over an impregnated palladium
catalyst at about 150.degree. C. and about 15 bar.
It is an object of the present invention to provide a process for the
selective hydrogenation of dienes in which
a highly effective hydrogenation of the dienes occurs
aromatics are essentially not hydrogenated
a stable, inexpensive catalyst is used
the process can be automatically controlled simply and effectively, and
the process can be conducted in a simple manner in existing plants and
refineries.
We have found that this object is achieved by a process for the selective
hydrogenation of dienes in diene-containing feed streams, which comprises
hydrogenating such a diene-containing feed stream over a nickel-containing
precipitated catalyst at from 40 to 100.degree. C., a pressure of from 3
to 20 bar and a WHSV of from 1 to 10 kg/(l.times.h) in the presence of
free hydrogen.
According to the present invention it has been found that nickel-containing
precipitated catalysts which are known per se from EP-A 0 672 452 allow
very effective selective hydrogenation of dienes, with the hydrogenation
using this catalyst being carried out with high reformate space velocities
over the catalyst and under low-pressure and low-temperature conditions.
Using the process of the present invention, it is possible, during
operation under low pressure and temperature conditions and a high
reformate throughput, to feed the hydrogen into the hydrogenation reactor
in such a way that the amount fed in is regulated as a function of the
dienes being hydrogenated.
PRECIPITATED NICKEL CATALYST
The precipitated nickel catalysts used according to the present invention
are described in EP-A 0 672 452. These catalysts consist essentially of
from 65 to 80% of nickel calculated as nickel oxide, from 10 to 25% of
silicon, calculated as silicon dioxide, from 2 to 10% of zirconium,
calculated as zirconium oxide and from 0 to 10% of aluminum, calculated as
aluminum oxide, with the proviso that the sum of the contents of silicon
dioxide and aluminum oxide is at least 15% (percentages in percent by
weight, based on the total mass of the catalyst). They are prepared by
addition of an acid aqueous solution of nickel, zirconium, and, if
desired, aluminum salts to a basic aqueous solution of silicon and, if
desired, aluminum compounds, with the pH being lowered to at least 6.5 and
subsequently being adjusted to from 7 to 8 by an addition of further basic
solution, isolating the solid thus precipitated, drying, shaping and
calcining.
The catalysts used according to the present invention preferably comprise
from 70 to 78% of nickel, from 10 to 20% of silicon, from 3 to 7% of
zirconium, and from 2 to 10% of aluminum.
Preference is given to using catalysts which comprise only nickel as
catalytically active metal. In particular, catalysts which are free of
palladium can be used.
In addition to the oxides specified, the catalysts can contain promoters in
amounts of up to 10%. These are compounds such as CuO, TiO.sub.2, MgO,
CaO, ZnO, and B.sub.2 O.sub.3. However, preference is given to catalysts
which contain no promoters.
The catalysts applied in the present invention are prepared starting from
aqueous acid solutions of nickel, zirconium, and, if desired, aluminum
salts. Suitable salts are organic and inorganic salts such as acetates,
sulfates, carbonates, but preferably nitrates of the metals specified. The
total content of metal salts is generally from 30 to 40% by weight. Since
the later precipitation of the metals from the solution is virtually
quantitative, the concentration of the individual components in the
solution depends only on the content of this component in the catalyst to
be prepared. The aqueous solution is adjusted to a pH of below 2 by
addition of a mineral acid, preferably nitric acid.
This solution is, advantageously whilst stirring, introduced into an
aqueous basic solution comprising silicon compounds and, if desired,
aluminum compounds. This solution comprises, for example, alkali metal
hydroxide or preferably sodium carbonate, generally in amounts of from 15
to 40% by weight, based on the solution. The pH is generally above 10.
Suitable silicon compounds are water glass, which is preferred, and also
SiO.sub.2. The silicon content of the solution is advantageously from 0.5
to 4% by weight. In addition, the solution can, if desired, contain
aluminum compounds in the form of oxidic solids, although it is preferred
to add aluminum salts only to the acid solution. The addition of the acid
solution to the basic solution is generally carried out at from 30 to
100.degree. C., preferably at from 60 to 80.degree. C. It is generally
carried out over a period of from 0.5 to 4 hours.
A sufficient amount of the acid solution is added for the pH to drop to at
least 6.5, thus precipitating insoluble compounds. Preference is given to
a range from 4.0 to 6.5, particularly preferably from 5.5 to 6.5. Lower pH
values are possible, but give no discernible advantage for the catalysts
thus prepared. In general, this pH is maintained for from 1 to 60 minutes,
depending on the amount of the solutions used, then adjusted to from 7 to
8 by addition of further basic solution and the precipitation of the metal
compounds is completed at this pH.
If catalysts containing promoters are desired, it is advantageous to add
soluble metal salts as precursors for the promoters to one of the
solutions described, to coprecipitate these metals and to further process
the precipitation product thus obtained. However, the promoters can also
be added as solids to the precipitation solution.
The precipitated product is isolated, for example, by filtration. In
general, this is followed by a washing step during which, in particular,
any alkali metal ions and nitrate ions entrained during the precipitation
are washed out. Subsequently, the solid thus obtained is dried, for which
purpose a drying oven or a spray dryer can be used for example, depending
on the amount of material to be dried. In general, the drying temperature
is from 100 to 200.degree. C. If desired, the above- mentioned promoters
can be mixed into the solid prior to the next process step. The dried
product is then preferably calcined, generally at from 300 to 700.degree.
C., preferably from 320 to 450.degree. C., over a period of from 0.5 to 8
hours.
For use according to the present invention, the calcined solid is shaped to
produce shaped bodies, for example by extrusion to give extrudates or by
tableting. For this purpose, peptizing agents such as nitric acid or
formic acid are added to the calcined solid in amounts generally from 0.1
to 10% by weight, based on the solid to be shaped. For tableting, graphite
can, for example, be used. The shaped bodies thus obtained are generally
calcined at from 300 to 700.degree. C., preferably from 350 to 500.degree.
C., for from 1 to 8 hours.
Hydrogenation Process
The process parameters used according to the present invention and the
preferred process parameters are shown in the table below.
Hydrogenation Process Parameters
______________________________________
Range Preferred range
______________________________________
Temperature 40-100 .degree.
50-80.degree. C.
Pressure 3-20 bar 5-12 bar
WHSV* 1-10 kg/(l .times. h) 3-7 kg/(l .times. h)
______________________________________
*Weight hourly space velocity
Feed Streams
The feed streams preferably used in the process of the present invention
comprise from about 15 to about 90% by weight of aromatics and up to about
5000 ppm by weight of dienes. The most preferred feed streams are
reformate streams.
In a particularly preferred embodiment of the process according to the
present invention, the hydrogen is fed into the hydrogenation step in a
regulated manner so that the amount of hydrogen fed in is approximately
that required for hydrogenating the dienes. The regulation is here
preferably carried out such that from 1 to 1.3 mol, preferably from 1 to
1.2 mol, particularly about 1.2 mol of hydrogen is fed in per mol of diene
structure in the feed stream.
Preference is given to carrying out the process using a catalyst comprising
from 65 to 80% by weight of nickel, from 10 to 25% by weight of silicon,
from 2 to 10% by weight of zirconium, from 0 to 10% by weight of aluminum,
all components calculated as oxides and percentages by weight based on the
total mass of the catalyst, with the proviso that the sum of the contents
of silicon dioxide and aluminum oxide is at least 15%.
Furthermore, it is preferred according to the present invention for
hydrogenated product to be separated in an extractive distillation step
into an aromatic hydrocarbon mixture and a non-aromatic hydrocarbon
mixture.
Finally, it is provided for and preferred according to the present
invention for the aromatic content of the mixture to be hydrogenated to be
increased prior to the selective hydrogenation by means of one or more
upstream distillation, extraction and/or extracted distillation steps.
Surprisingly, the nickel-containing precipitated catalysts described also
display a high selectivity in the hydrogenation of dienes in aromatic-rich
hydrocarbon mixtures when the process is configured such that the catalyst
is subjected to a high feed stream, especially reformate stream throughput
at low pressure and temperature and the hydrogen is fed into the reactor
in such a way that its amount is regulated as a function of the diene to
be hydrogenated.
The use of the hydrogenation step according to the present invention is
particularly useful in combination with a downstream extractive
distillation of the hydrogenated product to isolate the valuable
aromatics. It is already known that aromatic hydrocarbon mixtures can be
obtained selectively from aromatic/non-aromatic hydrocarbon mixtures by
extractive distillation, with the organic solvent used comprising a
high-boiling polar liquid (Ullman's Encyclopedia of Industrial Chemistry,
5th edition, vol. A3, page 490, Verlag Chemie). DE-A 20 40 025 discloses
the fact that N-substituted morpholines are particularly suitable as such
a selective solvent. The preferred solvent for the extractive distillation
step is NFM (N-formylmorpholine).
Accordingly, the compounds formed in the selective hydrogenation of the
reformate stream can be very simply separated from the aromatic
hydrocarbon mixture during the extractive distillation step. If the
hydrogenation conditions are too drastic (e.g. end-of-run conditions) or
the catalyst is too active, it is possible for aromatics to be
hydrogenated. The naphthenes thus formed are likewise removed from the
aromatic mixture during the extractive distillation step, so that high
purity is ensured without additional treatment with alumina.
The practical utility of the process of the present invention is
demonstrated by the example below. The starting hydrocarbon mixture used
was a benzene-rich reformate fraction. The purity in respect of diene
compounds present was tested by means of the wash color test in accordance
with ASTM D-848. The experimental reactor was operated in a downflow mode
under the following conditions:
temperature: T=60.degree. C.
pressure: PH.sub.2 =10 bar
throughput: WHSV=6 kg/(l.sub.Cat .times.h)
off-gas: 1.7 standard l/kg
______________________________________
Precipitated Ni
Impregnated Pd
catalyst* catalyst
(according to the (according to
Feed present invention) FR 2 720 754)
______________________________________
Wash color test
6 1 3
(in accordance with
ASTM D-848)
Loss of aromatics -- <0.1% by weight <0.1% by weight
______________________________________
*as described in EPA 0 672 452 with the following composition
N 75% by weight
Si 15% by weight
Al 5% by weight
Zr 5% by weight
(all as oxides)
This example shows that the diene compounds present in the reformate are
selectively hydrogenated by use of the nickel-containing precipitated
catalyst according to the present invention, which leads e.g. to the wash
color test value being improved without a high loss of aromatics.
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